As part of their Internet Medieval Sourcebook, Fordham University offers a section on medieval feudal oaths as part of a legal discussion of feudalism. Sources were created during the Middle Ages.
From the Internet Medieval Sourcebook:
The texts here have traditionally been used to explain the "feudal system". They may be better read and discussed, perhaps, as examples of how people created a variety a social and personal bonds in a society with few stable and accessible legal or governmental authorities. They do not represent a "system".
Oaths and Contracts
[Tierney 31.1] Fidelity Oaths.
[Tierney 31.2] Capitularies on Oaths.
[Tierney 33.1, Geary 25] Fulbert of Chartres: Letter on mutual obligations, 1020.
[Geary 26] Agreement between Count William V of Aquitaine and Hugh IV of Lusignan. [different translation than Geary]
Homages Paid by the Counts of Champagne, 12th Cent. [At Hillsdale]
John of Toul's Homage to the Count of Champagne, 13th Cent. [At Hillsdale]